JP2011-106377A discloses an engine comprising an injector which is configured to inject fuel into a cylinder and a spark plug which is configured to ignite air-fuel mixture in the cylinder. The injector and the spark plug are provided at an upper portion of a combustion chamber of the engine. The injector includes multiple injection ports. The injection ports include a inject port of which a central position is located closest to a central position of a discharge gap of the spark plug. In this engine, a distance between the central position of the central position of the discharge gap and that of the closest inject port is set in advance a certain distance.
The patent publication also discloses an engine control in which a high voltage is applied to the spark plug between after a lapse of a predetermined time from the start of fuel injection from the injector and the end of the fuel injection. To put it briefly, the engine control is a control in which an injection period is overlapped with an ignition period. The fuel splay immediately after the injection proceeds in the injection direction while taking away the surrounding air. Therefore, a low pressure part is formed in the injection period (entrainment). On the other hand, a discharge spark is generated on the discharge gap in the ignition period. Then, when the engine control in which an injection period is overlapped with an ignition period is performed, the discharge spark is attracted by the low pressure part. According to such attraction action, the ignitability of the air-fuel mixture formed around the spark plug can be improved.
In addition, the patent publication discloses an activation control of an exhaust gas cleaning catalyst at engine start as an application example of the attraction action. Although the patent publication does not refer to, the activation control of the exhaust gas cleaning catalyst is generally performed by setting the ignition period (i.e. an application period of the high voltage to the spark plug) on a retard side relative to compression top dead center TDC.
Suppose that when the engine control is applied to the general activation control, the fuel injection period is overlapped with the ignition period which is set on the retard side relative to the TDC. Therefore, according to the engine control, the same effect is expected as the engine control. However, since the activation control is performed during the engine start, combustion in the cylinder tends to unstable. When such an unstable combustion occurs frequently in cycles of the activation control, combustion fluctuation between cycles increase to affect performance of the engine.
The present disclosure addresses the above described problem, and an object of the present disclosure is to suppress combustion fluctuation between cycles when an engine control in which an ignition period is overlapped with a fuel injection period is applied to an activation control of an exhaust gas cleaning catalyst.